1. Field of the Invention
The present invention relates to a vehicle steering apparatus which supplies steering means with steering reaction force corresponding to a steering amount, which is the amount of a steering operation performed by the driver.
2. Description of Related Art
Known as one of steering apparatuses for vehicles is a steer-by-wire steering apparatus wherein a steering wheel which functions as steering means and a steering mechanism are not connected mechanically with each other. Such a steer-by-wire steering apparatus is disclosed in Japanese Patent Application Laid-Open No. H10-258751 (1998), for example. The steer-by-wire steering apparatus disclosed therein has a steering wheel arranged in a mechanically separated manner from a steering mechanism, and an actuator for steering (electric motor) is provided at the steering mechanism. The electric motor is driven in a controlled manner by controlling means constituted of a microprocessor on the basis of detection results of the steering amount of the steering wheel (steering angle and steering direction), thereby realizing steering corresponding to the steering amount of the steering wheel.
A reaction force actuator (electric motor) is attached to the steering wheel which is not connected mechanically with the steering mechanism. The reaction force actuator is driven in a controlled manner with reaction force instructing signals outputted from the controlling means on the basis of detection results of the steering amount of the steering wheel and the vehicle speed, for example. The reaction force actuator supplies the steering wheel with reaction force directing the steering wheel towards the neutral position thereof. The reaction force changes in intensity in response to changes in the steering amount and in the vehicle speed. Such a structure allows a driver to steer the vehicle with similar feeling to that of a general steering apparatus in which a steering wheel and a steering mechanism are connected mechanically with each other.
Drive of the reaction force actuator (electric motor) is controlled on the basis of vehicle information, such as the steering amount of the steering wheel (steering angle), a vehicle speed, a yaw rate and a lateral acceleration. Since the steering angle, vehicle speed, yaw rate or lateral acceleration seldom changes drastically in a short time, drive of the reaction force motor is controlled mainly on the basis of vehicle information within a low frequency band (a frequency between 2 Hz and 3 Hz or lower, for example). On the other hand, the roughness of the road surface or the like often changes in a short time, in a high frequency band (between 3 Hz and 15 Hz, for example). Since mainly used for drive control of the reaction force motor is vehicle information within a low frequency band, reaction force in response to the roughness of the road surface or the like cannot be transmitted to the driver satisfactorily.